UNH-IOL Fibre Channel Tutorial and Joy Jiang and Claudio DeSanti, The role of FCoE in I/O consolidation, Proceedings of the 2008 International Conference on Advanced Infocomm Technology
Scribed by Nishchay Sinha
Summary:
This lecture was our introduction to fiber channel protocol used in storage area network.The tutorial tersely discussed an idiot’s introduction to FC which is a new technology for SAN.It outlines the standardization efforts,various classes that exist across the FC and methodology of implementation.There are four FC layers FC0-4 with FC0 being the physical layer,FC-1 the framing layer,FC-2 the signaling layer ,FC-3 the services layer and FC-4 defining various applications like scsi,ip running atop FC.The topology of FC can be point to point or a distributed one.In case of distributed topology there is an initialization phase after which every device knows its physical address .FC supports hubs and fabrics also in its topology.Flow control is guaranteed loss less by mechanisms like buffer to buffer negotiated credits that lets transmitter only send a limited number of outstanding packets at a given time instant.Many classes of services are defined too but class 3 is only widely used as in SAN;Class 3 only uses buffer to buffer credits. FC uses 3 bytes addresses for port id,fabric id information.There may be an arbitrated loop id also.The transmission hierarchy is 8B/10B encoded characters ,four of which make a transmission word.A frame is top transmission hierarchy which can have up to 2112 bytes of payload and 36 bytes of overhead.
The role of FCoE in I/O consolidation paper discusses the consolidation of disparate SAN networks like LAN and SAN onto a converged network of FC using convergence protocol like FCOE.This is because of low cost ,lossless and speed properties of FC that suits all the untied technologies.Convergence is important as this will lead to less power consumption and lower cost of cabling and hardware requirements.Another competing technology iSCSI, is dependent on TCP (apart from being stateful and not scalable) and hence is unsuitable for SAN networks.
Discussion:
1.Storage is 2.5 billion industry.
2.SCSI works for many storage drives and single server but not for many servers accessing a single storage drive
3.Hard drives are 7500 rpm devices with capacity in orders of terbaytes.
4.FC(Fibre channel) has lots of classes discussed but only class 3 is generally used.
5.Concept of arbitrated loops to arbitrate control of a storage drive by many contending drivers.
6.Fibre channels assigns topological id in sets of switch id-area id-port id to drive.This makes routing easy as is location based.
7.Flogins(initial setup) assigns addresses to devices and plogins let access to storage drives.
8.Credits:buffer to buffer credits:This is a flow control mechanism in which two end points negotiate how many packets they are going to receive at a time from one another.By doing this they are able to prevent any loss of packets because of buffer overflow and this gives near zero loss probability to fiber channel.
9 Basic transaction in FC is very easy with a protocol write to negotiate buffer credits followed by data packets writes or reads and followed by a status message.The status message could indicate disk write errors.
10Framing is done at 32 bit boundary .
11.1 gb of FC carries 800mb of payload whereas 1 gb ethernet carries 1 gb data on wire.
12.As different os’s use different formatting it can lead to wrongful formatting.This leads to zoning in storage drives under FC.
13.Positive points about fibre channel protocol:Simple,lossless,cheaper,multipathing and load balancing,low state and fast.
14.Bad about FC:1.cant go long distances,2.interoperability issues,3.no congestion handling.4.only layer 2 protocol.5.inopportune economics due to prevalence of ethernet6.Tight control by EMC bad for free market and development.
15.FC is not inherently reliable but is implementation reliable.
16.I/o consolidation to FCOE so late?because of critical mass of FC devices in market that exist now.
17.FCOE is stateless and one to one mapping to Ethernet frame is possible
18 Differences between Ethernet and FCOE: packet sizes,duplex,frame size,loss less flow control,24/48 bit addresses..
19.Pause frames in FCoE to do loss less flow control.
20.No length field in FCOE packets can ease cut through router deployment.
Critique:
This was more of a tutorial overview of a new topic and hence a critical analysis is bit difficult.Never the less the tutorial was really terse and difficult to understand.The elucidation by Tom was really great in getting a somewhat better understanding of this technology.
